A-4 Analog Output [T-Series Datasheet] | LabJack

A-4 Analog Output [T-Series Datasheet]

Specifications for analog output channels (DAC0 and DAC1) are shown below.

T4

Table A4-1. T4 DAC Information.  All specs at room temperature unless otherwise noted.

 Conditions Min Typical Max Units Nominal Output Range [1] No Load 0.01 4.98 Volts @ ±2.5 mA 0.30 4.69 Volts Resolution 10 Bits Absolute Accuracy 5% to 95% ±0.15 % FS ±7.5 mV Integral Linearity Error ±1 counts Differential Linearity Error ±0.1 ±0.5 counts Noise [2] ±1 counts Source Impedance [3] 110 ±10 Ω Current Limit [4] Max to GND 32 mA Time Constant 1 μs [1] Maximum and minimum analog output voltage is limited by the supply voltages (`VS` and `GND`). The specifications assume `VS` is 5.0 volts. Also, the ability of the DAC output buffer to driver voltages close to the power rails, decreases with increasing output current. [2] Specified with no load and set to 0 V. Noise will increase with load and voltage, to a maximum of 3 counts @ 4V with a 100 Ω load. The DAC's ability to reject noise decreases as the output voltage nears the Vs supply. [3] The source impedance is a combination of fixed resistance and the impedance from the output buffer. The impedance from the buffer will vary depending on the operating conditions. When set to 4 V with a 100 Ω load, Rs is ~ 112 Ω. When set to 4 V with a 10 kΩ load, Rs is ~110 Ω. [4] The output buffer will limit current to about 30 mA and can maintain this value continuously without damage. Take, for example, a 1.5 ohm resistor from `DAC0` to `GND`, with the internal source impedance of 110 ohms, and `DAC0` set to 4.5V. A simple calculation would predict a current of `4.5/(110+1.5) = 40 mA`, but the output buffer will limit the current to 32 mA.

T7

Table A4-2. T7 DAC Information.  All specs at room temperature unless otherwise noted.

 Conditions Min Typical Max Units Nominal Output Range [5] No Load 0.01 4.99 Volts @ ±2.5 mA 0.25 4.75 Volts Resolution 12 Bits Absolute Accuracy 5% to 95% FS ±0.06 % FS Integral Linearity Error ±1.5 ±2 counts Differential Linearity Error ±0.25 ±0.5 counts Noise [6] ±100 μV Source Impedance [7] 50 Ω Current Limit [8] Max to GND 20 mA Time Constant 4 μs [5] Maximum and minimum analog output voltage is limited by the supply voltages (`VS` and `GND`). The specifications assume `VS` is 5.0 volts. Also, the ability of the DAC output buffer to driver voltages close to the power rails, decreases with increasing output current. [6] With load, the noise increases if operating too close to `VS`. With a 1000 ohm load, noise increases noticeably at 4.4V and higher. With a 330 ohm load, noise increases noticeably at 3.7V and higher. With a 100 ohm load, noise increases noticeably at 2.7V and higher. [7] For currents up to about 8mA, this source impedance dominates the error due to loading. For example, if you load `DAC0` with a 1000 ohm resistor from `DAC0` to `GND`, and set `DAC0` to 3.0V, the actual voltage at the `DAC0` terminal will be about `3.0*1000/(50+1000) = 2.86V`. For currents > 8mA, you increasingly get added droop due to the ability of the output buffer to drive substantial current close to the power rails. [8] The output buffer will limit current to about 20mA and can maintain this value continuously without damage. Take, for example, a 100 ohm resistor from `DAC0` to `GND`, with the internal source impedance of 50 ohms, and `DAC0` set to 4.5V. A simple calculation would predict a current of `4.5/(50+150) = 30mA`, but the output buffer will limit the current to 20mA. A simple calculation taking into account only the voltage droop due to the internal 50 ohm resistance would predict a voltage at the `DAC0` terminal of `4.5*100/(50+100) = 3.0V`, but since the current is limited to 20mA the actual voltage at `DAC0` would be more like `100*0.02 = 2.0V`.